1187

Abstract

Case Reports: Previous studies have reported conflicting results regarding the effect of serum hyperbilirubinemia on pulse oximetric accuracy. While initial studies demonstrated an underestimation of true O2 saturation by pulse oximetry, subsequent studies have suggested that hyperbilirubinemia does not influence pulse oximetric accuracy. However, recent observations in the bone marrow transplant literature suggest that hyperbilirubinemia is associated with an overestimation of true O2 saturation as measured by pulse oximetry. Aim: To assess whether excessive hyperbilirubinemia in liver disease is associated with an overestimation of true oxygen saturation as measured by pulse oximetry. Methods: Six patients with decompensated cirrhosis, severe hyperbilirubinemia, and hypoxemia due to acute lung injury or hepatopulmonary syndrome, were analyzed. Hemoglobin oxygen saturations obtained via standard pulse oximetry and arterial blood gas (ABG) analysis using arterial lines were compared. Co-oximetric analysis was performed to measure carboxy-Hgb and met-Hgb levels to assess for dyshemoglobinemia induced pulse oximetric inaccuracy. In addition, in vitro spectral analysis of bilirubin absorption in fetal bovine serum (FBS) was performed to evaluate for a mechanistic rationale for the potential influence of bilirubin on pulse oximetric accuracy. Results: The measurements demonstrated that pulse oximetric values consistently overestimated true oxygen saturation, with the degree of overestimation ranging from 10 to 35%. Measurements of carboxy –Hgb and met-Hgb were within normal limits, thereby ruling out these dyshemoglobinemias as potential etiologies of overestimation. In vitro spectral analysis of bilirubin in fetal bovine serum (FBS) demonstrated a concentration-dependent interference in absorption in the wavelengths corresponding to deoxy-hemoglobin quantification. Conclusions: This case series suggests that excessive hyperbilirubinemia in the setting of cirrhosis can cause an overestimation of true oxygen saturation as measured by pulse oximetry. Furthermore, our spectral analysis suggests that bilirubin may influence the accuracy of pulse oximetry by interfering with and underestimating the quantification of deoxy-Hgb, which in turn, can cause overestimation of oxygenated Hgb quantification. These results suggest that in cirrhotic patients with hyperbilirubinemia, and especially those at risk for hypoxemia, ABG analysis should be performed to corroborate pulse oximetric measurements.